2 Site HistorySite is on the upper end of the Watts Bar Reservoir just north of Interstate 40.The coal-fired generating station was constructed in the 1950’s.The generating station draws cooling water from the Emory River and discharges to the Clinch River which in turn enters the Tennessee River.Slack water from the Watts Bar Dam envelopes the mouth of both the Clinch and the Emory River.Prior to the ash spill the main channel of the Emory River at the Site is approximately 30-feet deep.

4 Fly Ash Storage HistoryOriginally, ash was sluiced wet from the plant to a basin constructed in the Watts Bar ReservoirThe basin is contained by a clay dike that is raised three times to eventually impound 60-feet thickness of ashStarting in the 1980’s, accumulating ash was dredged and stored in an engineered storage cell constructed on top of the filled basinBy late 2008, the storage cell reached 60-feet height and covered approximately 90 acres

6 Ash ReleaseEarly morning of December 22, 2008 a dike failure near the northwest corner of ash storage results in static liquefaction of nearly 2/3 of the stored ashThe flowing ash water mixture flows into the Emory River moving both upstream and downstreamWhen the flow stopped, the main channel of the river was filled with ashThe Emory flows around the ash in a shallow area of the Watts Bar Impoundment

7 Aerial December 23, 2008 Day After Ash SpillMain channel filled with over 30 feet of ashEmory River flowing around the ash in shallow impounded water of Watts Bar ReservoirAsh Storage Cell

8 What is Fly Ash?Fly ash is the fine residue from the burning of coal that escapes with the combustion gas and is removed by air treatment equipmentWith bottom ash it is 10% by weight of the coal at KingstonThe majority of fly ash is within the size range of 100 to 1 micron (fine sand and silt particle size)The particles are spherical with some particles forming as hollow spheres known as cenospheresBecause of the cenospheres the solid specific gravity may be lower than for earth minerals (as low as 2.0)

9 Specific gravity of fly ash at Kingston in the 2.2 -2.4 rangeFly Ash Magnified 2000xFly Ash consists primarily of oxides of silicon, aluminum iron and calcium (85-90% by weight).Magnesium, potassium, sodium titanium, and sulfur oxides make up most of the remaining weight with traces of heavy metals .Specific gravity of fly ash at Kingston in the rangeSource: Federal Highway Administration

11 Purpose of Ash RemovalTime Critical Removal was to open Main Thalweg of the Emory RiverNon-Time Critical work on land and in embayments separated from Time Critical by a landside rock berm.Opening river channel to approximate original contours was goal of removalIt was recognized that further dredging may be required in later stages of the ash recovery after completion of the Time Critical Removal

13 Time Line for ProgressIt was considered time critical that the main channel be open by no later than Spring 2010.Avoid impact from the Spring flood season of 2010.Besides the logistics of dredging and dewatering the ash, the logistics of removing the ash from the site had to be resolved to complete the removal.It was estimated that the time critical work involved million cubic yards of ash.

14 Ash Recovery by Hydraulic DredgingExperience at the site was already good with hydraulic dredging for building the ash storage cellIt was believed that the ash would settle out quickly in a rim ditch removal method as was used to build the ash storage cellThe production rate using mechanical dredging was slower with the same level of manpower and equipmentThe existing ash pond and sluice ditch were available for hydraulic operation

19 Results of Pilot Test Average percent dry solids to the ditch 8.4%Flocculent Settling Rate 14 in/hourSolids Content after 12 hours of quiescent settling 65%Rim Ditch removal rate of 90% when the flow was under 10,000 gpmWith higher flows more solids to the Sluice TrenchConstant agitation of the Rim Ditch by backhoe results in a thickened solids content of 30-35% in the water column of the ditch.

23 Dredging Results10-inch pump dredges were too small to complete the work within the timeline goalsSubstantial problems with plugging from trees and other debrisAsh is very abrasive and results in heavy maintenance impact on operation.Three 10-inch dredges moved on average 4,000 cubic yards per dayProblems with dredges from fast river currentsAt end of pilot 375,000 cubic yards removed

24 Full Scale Dredging OperationCompetitive bidding to dredge at full-scale operation defined as completing 1.5 million cubic yards to open the main channel by February 28, 2010.Required production rate of approximately 12,000 cubic yards per day 6-days per weekCompetitive bidding for the work with Sevenson Environmental selected for the work.Dredging equipment initially on site was one 20-inch cutterhead dredge and one 14-inch cutterhead dredgeLater supplemented with a 16-inch cutterhead dredge

25 Subcontracted by Sevenson to L.W. Matteson20-Inch DredgeSubcontracted by Sevenson to L.W. Matteson

32 ObservationsRim Ditch operated at 20 MGD 100% above its hydraulic capacity determined during the pilot testEfficiency of the Rim Ditch was reduced from the pilot operation and the fly ash pond was required to store ashWith the use of a coagulent, the stilling basin continued to produce acceptable water for discharge (permit limit average TSS of 29 ppm)Using a dredge to remove ash from the fly ash pond and cycle back to the Rim Ditch provided little improvement of performance

36 Summary of Full Scale PerformanceAsh Pond filled at rate of approximately 4,000 yd3/day (approximately 1/3 of the daily in-river dredge volume)February 1, million cubic yards removed under full scale dredgingAsh Pond removal was undertaken in January to develop new pond capacity to complete Emory River removal goalGoal of opening river channel is obtained with very little reserve capacity in ash pond